When a biological component such as blood or a body fluid comes into contact with a surface of a material used in a medical device, the material is recognized as a foreign matter and causes adhesion of platelets and proteins, deterioration of material performance, and even biological reactions to lead to serious problems. For example, in a blood purifier, adhesion of proteins and platelets deteriorates fractionation performance and water permeability. In particular, in a continuous renal replacement type blood purifier used for the treatment of acute renal failure, it is important to suppress adhesion of platelets and proteins and prolong the usable time of the blood purifier because the blood purifier is continuously used for one day to several days. To deal with such an issue, attempts have been made to make the surface of a material used in a medical device hydrophilic, and various studies have been made.
For example, a method is known in which polyvinylpyrrolidone, which is a hydrophilic polymer, is mixed in polysulfone at the stage of a membrane-forming stock solution and the resultant mixture is molded so that hydrophilicity is imparted to the membrane and contamination is suppressed. However, that method has restrictions in that a large amount of a hydrophilic polymer should be incorporated into the membrane-forming stock solution to impart hydrophilicity to the surface, and the hydrophilic polymer is limited to a polymer compatible with the base polymer.
Meanwhile, Japanese Patent Laid-open Publication No. 6-238139 discloses a method of bringing a polysulfone-based separation membrane into contact with a solution of a hydrophilic polymer such as polyvinylpyrrolidone, and then forming a coating layer insolubilized by radiation crosslinking.
In addition, Japanese Patent Laid-open Publication No. 2009-262147 and Published Japanese Translation No. 2005-518841 disclose a method of introducing a copolymer composed of a hydrophilic unit and a hydrophobic unit typified by a vinylpyrrolidone/vinyl acetate copolymer onto the surface.
The method described in Japanese Patent Laid-open Publication No. 6-238139, however, has a problem that it is difficult to form a coating layer because the interaction between a hydrophilic polymer such as polyvinylpyrrolidone and a polysulfone-based polymer that is a hydrophobic polymer is weak.
On the other hand, in the methods described in Japanese Patent Laid-open Publication No. 2009-262147 and Published Japanese Translation No. 2005-518841, a hydrophobic unit interacts with a hydrophobic base material, whereby the introduction efficiency of the copolymer is increased and the surface can be efficiently hydrophilized. Therefore, it is clear that the methods suppress the adhesion of platelets and proteins as compared to when only a hydrophilic polymer such as polyvinylpyrrolidone is introduced onto the surface.
Even in the methods described in Japanese Patent Laid-open Publication No. 2009-262147 and Published Japanese Translation No. 2005-518841, however, when the copolymer is used in a medical device to be used in contact with a biological component such as blood for a long period of time as in a continuous renal replacement type blood purifier, blood coagulation and protein adhesion progress with time due to the long-time contact with the biological component such as blood, which may eventually lead to clogging and render the medical device unusable.
It could therefore be helpful to provide an anti-thrombotic copolymer capable of suppressing adhesion of platelets and proteins even when in contact with a biological component such as blood for a long period of time, and a medical device, a separation membrane module for medical use, and a blood purifier including the copolymer that are high in blood compatibility.